expression
for any reason; no matter what the reason
Used in negative or restrictive contexts to mean 'for no reason whatsoever' or 'regardless of the reason'. Often appears as いかなる理由があっても or いかなる理由でも.
いかなる理由があっても、暴力は許されない。
Violence is not acceptable for any reason whatsoever.
いかなる理由でも、遅刻は遅刻だ。
No matter what the reason, being late is being late.
Combination of the formal interrogative いかなる (how, what kind of) and the noun 理由 (reason). いかなる derives from classical Japanese 如何なる, a literary form still used in formal modern contexts.